Mannosidosis, an inherited lethal nervous disease of Angus cattle, is a lysosomal storage disease due to a deficiency of lysosomal alpha- mannosidase. It is a general model for studying lysosomal storage diseases of children and a specific model, and being used as such, for studying human mannosidosis. It is planned to study alpha-mannosidase isoenzymes and to extract and purify lysosomal alpha-mannosidase. This would be used to prepare an antibody to be used for developing an assay technique and to study the product of the defective gene in mannosidosis. Purified alpha-mannosidase would be used to study some of the basic problems associated with enzyme therapy in this type of disease.